Dellorto Frusteration
07-31-10, 10:01 AM
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Dellorto Frusteration
So I just finished my dellorto DHLA 40 swap. I went by the Gruntled write up for the 48 but i bought a bunch more idle and main jets since my carb is a bit different. So here if my problem.
The car is bogging horribly. I cannot give the car more than a tiny amount of throttle or else the motor essentially stalls and wont continue to run unless i let off the gas. No matter the rpm or jets it always bogs. Its also not a bog from when i hit the pedal so its not looking like the accelerator pump either. I've tried running it both with a regulator set at 2.5 psi and bypassing it and running off the stock fuel pump (slightly more psi). Didn't make a difference either.
Help!
The car is bogging horribly. I cannot give the car more than a tiny amount of throttle or else the motor essentially stalls and wont continue to run unless i let off the gas. No matter the rpm or jets it always bogs. Its also not a bog from when i hit the pedal so its not looking like the accelerator pump either. I've tried running it both with a regulator set at 2.5 psi and bypassing it and running off the stock fuel pump (slightly more psi). Didn't make a difference either.
Help!
07-31-10, 11:16 AM
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Jolly Green Giant
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1. Make sure you list ALL MODS pertaining to the subject which in this case is everything you've done to the engine.
2. What jets are you running?
3. Do you have an a/f gauge? Even a cheap narrow band can be a great indicator if you're running lean or rich though it will be far from exact.
4. Is the car completely warm when you tried to drive it? My car will do the same thing if you give it any more than 1/4 throttle when its stone cold.
5. After it "stalls" like that when you take your foot off does it return back to normal like nothing happened? If so it sounds like your running lean, excessively rich condition like that would probably cause a stutter for some time after until all the excess fuel flushes out.
2. What jets are you running?
3. Do you have an a/f gauge? Even a cheap narrow band can be a great indicator if you're running lean or rich though it will be far from exact.
4. Is the car completely warm when you tried to drive it? My car will do the same thing if you give it any more than 1/4 throttle when its stone cold.
5. After it "stalls" like that when you take your foot off does it return back to normal like nothing happened? If so it sounds like your running lean, excessively rich condition like that would probably cause a stutter for some time after until all the excess fuel flushes out.
07-31-10, 04:02 PM
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i'm becoming familiar with the weber IDA, so some of this might be a little different in detail.
1. the best recommendation ive seen so far is to tune from the bottom up, ie start with the idle, and work up to WOT.
step 1. since the carb is a mechanical device, it MUST be set up right. all the passages clean, jets clean. you can check for the throttle plates being synchronized, and that they are in the right place at idle.
step 2. the float level needs to be set right. i would start with the lower fuel pressure, but if the needle and seat are good, it won't matter.
step 3. this is a jusdgement call, but i would set the idle speed and mixture screws like RB says. i would also start with their idle jet and holder. the main jet em tube and stuff shouldn't matter, on the IDA you can leave em out, and it'll run up to like 3500rpms
step 4. start the thing! let it warm up and adjust the idle mixture. at idle you just set the mixture for best idle speed, and a little leaner. you can do this at higher rpms too, but an o2 sensor, or wideband would help. now is also a good time to look for vacuum leaks. if the idle mixture screws are too far in or out, then go up or down a jet size. you want the idle jet to give an idle mixture that is close to optimum at the default position of the idle speed screw.
step 5. having found the best idle speed/mixture, use the idle speed screw to start increasing the engine speed. you can use the idle mixture screws to see if its too rich or too lean at different "idle speeds" on mine i used 1/2 turns of the idle speed screw, which is like 400rpm,900rpm, 1400, 2000, and like 2400.
5A, i find it helps to write this stuff down, as it can get to be a lengthy process. if you have an o2 sensor/wideband, having actual numbers to correlate the rpms with would be nice. ideally you'd want to try a few idle jet holders, and maybe a couple idle jets. once you get in the ball park, go drive it!
6. once you get the idle-20% throttle idle circuit sorted, then you can start on the mains. procedure is kind of the same. i would start with the RB fuel jet and EM tube and the smallest air you have. it should be rich, witch is safe, and you can lean it out
1. the best recommendation ive seen so far is to tune from the bottom up, ie start with the idle, and work up to WOT.
step 1. since the carb is a mechanical device, it MUST be set up right. all the passages clean, jets clean. you can check for the throttle plates being synchronized, and that they are in the right place at idle.
step 2. the float level needs to be set right. i would start with the lower fuel pressure, but if the needle and seat are good, it won't matter.
step 3. this is a jusdgement call, but i would set the idle speed and mixture screws like RB says. i would also start with their idle jet and holder. the main jet em tube and stuff shouldn't matter, on the IDA you can leave em out, and it'll run up to like 3500rpms
step 4. start the thing! let it warm up and adjust the idle mixture. at idle you just set the mixture for best idle speed, and a little leaner. you can do this at higher rpms too, but an o2 sensor, or wideband would help. now is also a good time to look for vacuum leaks. if the idle mixture screws are too far in or out, then go up or down a jet size. you want the idle jet to give an idle mixture that is close to optimum at the default position of the idle speed screw.
step 5. having found the best idle speed/mixture, use the idle speed screw to start increasing the engine speed. you can use the idle mixture screws to see if its too rich or too lean at different "idle speeds" on mine i used 1/2 turns of the idle speed screw, which is like 400rpm,900rpm, 1400, 2000, and like 2400.
5A, i find it helps to write this stuff down, as it can get to be a lengthy process. if you have an o2 sensor/wideband, having actual numbers to correlate the rpms with would be nice. ideally you'd want to try a few idle jet holders, and maybe a couple idle jets. once you get in the ball park, go drive it!
6. once you get the idle-20% throttle idle circuit sorted, then you can start on the mains. procedure is kind of the same. i would start with the RB fuel jet and EM tube and the smallest air you have. it should be rich, witch is safe, and you can lean it out
08-01-10, 01:23 AM
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Mods are as follows:
Rebuilt motor with 4k on it, cat delete, racingbeat intake (one piece) and the dellorto dhla 40, other than that the rest it all stock. Vac leaks are nil, and idle is fantastically smooth.
It makes no difference what jets I'm running i've gone from 150-250 (in increments of 10) and none of them appear to make a difference. The rest of the jets/holders/tubes are the ones RB reccomends to use in the DHLA48
The stutter appear to happen as i'm leaving the idle circuit. I can drive the car on 20% throttle no problem, but if i give it any more gas, the motor struggles (carb gets loud and you can hear a different tone from it) and there in no acceleration at all and often times it actually causes me to slow down if I put the pedal to the floor.
I'll try to get some video tomorrow to give you a better idea of whats going on.
Rebuilt motor with 4k on it, cat delete, racingbeat intake (one piece) and the dellorto dhla 40, other than that the rest it all stock. Vac leaks are nil, and idle is fantastically smooth.
It makes no difference what jets I'm running i've gone from 150-250 (in increments of 10) and none of them appear to make a difference. The rest of the jets/holders/tubes are the ones RB reccomends to use in the DHLA48
The stutter appear to happen as i'm leaving the idle circuit. I can drive the car on 20% throttle no problem, but if i give it any more gas, the motor struggles (carb gets loud and you can hear a different tone from it) and there in no acceleration at all and often times it actually causes me to slow down if I put the pedal to the floor.
I'll try to get some video tomorrow to give you a better idea of whats going on.
08-01-10, 02:24 AM
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Mods are as follows:
Rebuilt motor with 4k on it, cat delete, racingbeat intake (one piece) and the dellorto dhla 40, other than that the rest it all stock. Vac leaks are nil, and idle is fantastically smooth.
It makes no difference what jets I'm running i've gone from 150-250 (in increments of 10) and none of them appear to make a difference. The rest of the jets/holders/tubes are the ones RB reccomends to use in the DHLA48
The stutter appear to happen as i'm leaving the idle circuit. I can drive the car on 20% throttle no problem, but if i give it any more gas, the motor struggles (carb gets loud and you can hear a different tone from it) and there in no acceleration at all and often times it actually causes me to slow down if I put the pedal to the floor.
I'll try to get some video tomorrow to give you a better idea of whats going on.
Rebuilt motor with 4k on it, cat delete, racingbeat intake (one piece) and the dellorto dhla 40, other than that the rest it all stock. Vac leaks are nil, and idle is fantastically smooth.
It makes no difference what jets I'm running i've gone from 150-250 (in increments of 10) and none of them appear to make a difference. The rest of the jets/holders/tubes are the ones RB reccomends to use in the DHLA48
The stutter appear to happen as i'm leaving the idle circuit. I can drive the car on 20% throttle no problem, but if i give it any more gas, the motor struggles (carb gets loud and you can hear a different tone from it) and there in no acceleration at all and often times it actually causes me to slow down if I put the pedal to the floor.
I'll try to get some video tomorrow to give you a better idea of whats going on.
08-01-10, 03:11 AM
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Jolly Green Giant
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I believe that would narrow it down to fuel delivery being not a high enough rate of flow from the pump even at the correct psi, or a more likely scenario of super low float bowls causing them not to fill up very far.
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08-01-10, 04:01 PM
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Looks Like I'm going to have to. I thought I'd give it a shot since the PSI was above the suggested range for the carb but maybe its something to do with GPH flow? How would I adjust my floats exactly? When I rebuilt it the movement they had was great and the needle and seat in it are brand new as well. Unfortunately there is also no looking glass for me to see the fuel level either.
Also what flow rate should I shoot for? Looks like most pumps I can grab at the shop are around 30-40gph
Also what flow rate should I shoot for? Looks like most pumps I can grab at the shop are around 30-40gph
Last edited by FunK73; 08-01-10 at 04:15 PM.
08-01-10, 04:52 PM
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Looks Like I'm going to have to. I thought I'd give it a shot since the PSI was above the suggested range for the carb but maybe its something to do with GPH flow? How would I adjust my floats exactly? When I rebuilt it the movement they had was great and the needle and seat in it are brand new as well. Unfortunately there is also no looking glass for me to see the fuel level either.
Also what flow rate should I shoot for? Looks like most pumps I can grab at the shop are around 30-40gph
Also what flow rate should I shoot for? Looks like most pumps I can grab at the shop are around 30-40gph
i don't know about the Dell, usually there is a measurement or tool or something to set the floats
08-01-10, 05:24 PM
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Thankfully Installer put this together not to long ago which should cover just about anything you'll need to know about the dell, there should a post in there somewhere about float adjustments and how to set it https://www.rx7club.com/forum/showthread.php?t=896075
08-01-10, 08:16 PM
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Well I went through and adjusted my floats. Its now sitting 27mm from the top just like installer said. However, the problem persists. Does it still seem like it would be an issue of the fuel pump flow rate?
Heres a video of it happening. This is after I adjusted the floats and the engine was fully warm. Sorry about the clutch fan noise, hopefully you can hear the carb over it.
http://www.youtube.com/watch?v=j17GXXxtV9s
Heres a video of it happening. This is after I adjusted the floats and the engine was fully warm. Sorry about the clutch fan noise, hopefully you can hear the carb over it.
http://www.youtube.com/watch?v=j17GXXxtV9s
08-01-10, 08:32 PM
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That actually sounds like your main jets aren't even working, idle and light throttle would suggest that the progression ports are fine but once it switches to the main jets nothing happens.
Here's a good link to diagram/explination of Dellorto starting, idle, light throttle and WOT.
http://www.motorcyclecarbs.com/Dello..._W168C1334.cfm
Here's a good link to diagram/explination of Dellorto starting, idle, light throttle and WOT.
http://www.motorcyclecarbs.com/Dello..._W168C1334.cfm
08-01-10, 09:08 PM
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So where should i go from here? I should also mention this carb was run with leaded fuel back in the day but was soaked for a day and a half in carb cleaner before assembly.
08-01-10, 10:09 PM
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The only thing I can think of personally is that there is possibly a blockage in the bottom of the bowl down by #37 where the fuel is sucked up into the jets or in #36 where it leads to the barrells.
Did you actually rebuild the carb? or just soak it, take it apart, clean it and put it back together?
Another good check would be to take the air filter off, look down the barrells and open the throttle to see if you even have fuel flowing into the venturi when you open it past like 1/4....that should tell you right then and there if there is a blockage or if it's possibly a matter of what e-tubes you used or whatever [hence why I asked what jets and such you were using].
Did you actually rebuild the carb? or just soak it, take it apart, clean it and put it back together?
Another good check would be to take the air filter off, look down the barrells and open the throttle to see if you even have fuel flowing into the venturi when you open it past like 1/4....that should tell you right then and there if there is a blockage or if it's possibly a matter of what e-tubes you used or whatever [hence why I asked what jets and such you were using].
08-01-10, 10:14 PM
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Well i soaked it, cleaned it, all new jets, and a rebuild kit. I dont suppose this would be caused by my venturis being off in the tunnels slightly, blocking the fuel to spray through them?
I'll have to give that jet/emulsion tube a look tomorrow.
I'll have to give that jet/emulsion tube a look tomorrow.
08-01-10, 10:27 PM
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Hopefully they're not crooked, since there is a groove on them if i recall correctly. Thanks for all the help by the way. I'll do some investigating when its day light again and the neighbors aren't sleeping.
08-01-10, 10:39 PM
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No problem, glad to help...or atleast try to 
My dell had me stumped for nearly a month back in december when the car started running extremely rough under light throttle and it only got worse, I thought it was EVERYTHING from the MSD, to the Engine to the Carb itself...turned out to be a vac leak between the carb body and the manifold.
I must have had that carb off the engine atleast 5 times and had parts off it checking things and what not countless times.
Where did you order your kit from? I am actually in need of a new float for mine and I know of a few overseas companies but am always looking for new sources.
My dell had me stumped for nearly a month back in december when the car started running extremely rough under light throttle and it only got worse, I thought it was EVERYTHING from the MSD, to the Engine to the Carb itself...turned out to be a vac leak between the carb body and the manifold.
I must have had that carb off the engine atleast 5 times and had parts off it checking things and what not countless times.Where did you order your kit from? I am actually in need of a new float for mine and I know of a few overseas companies but am always looking for new sources.
08-01-10, 10:44 PM
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from dellorto directly in the UK. Takes about a week to get the parts. I ordered things from Dell, a guy in Italy, and most of my jets from CB Performance in California
08-01-10, 11:50 PM
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does the accelerator pump work? take the filter off and look in there when its running, you should be able to CAREFULLY look in there and see the accelerator pump shot and then see the mains start to meter fuel.
08-02-10, 08:28 AM
#21
Waffles - hmmm good
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First get a good fuel pump. The stock one can barely feed a Nikki much less a good
sized Dell. You want a low pressure, high flow rate pump. You only need about 2.5
psi but at least 50 gph for the pump. I'm using a Carter 4070 and it works very
well.
http://www.jegs.com/i/Carter/180/P4070/10002/-1
Also what venturies are you running? For a stock port 12a on a 48 the venturies
are around 36 or 38, can't remember I'd have to look. You will need similiar
because 40 will still be too big for a stock port.
I know for the 48 the measurement for the bowl drop is done holding the top
vertically and as the bowl tang just pushes the needle valve in it should be
around 15 mm, not 27. If you have it at 27 your float bowls won't have hardly
any fuel in them. It sounds like your getting no fuel either on your accel pump
or the primaries. Do the visuals like suggested to see which is not squirting.
sized Dell. You want a low pressure, high flow rate pump. You only need about 2.5
psi but at least 50 gph for the pump. I'm using a Carter 4070 and it works very
well.
http://www.jegs.com/i/Carter/180/P4070/10002/-1
Also what venturies are you running? For a stock port 12a on a 48 the venturies
are around 36 or 38, can't remember I'd have to look. You will need similiar
because 40 will still be too big for a stock port.
I know for the 48 the measurement for the bowl drop is done holding the top
vertically and as the bowl tang just pushes the needle valve in it should be
around 15 mm, not 27. If you have it at 27 your float bowls won't have hardly
any fuel in them. It sounds like your getting no fuel either on your accel pump
or the primaries. Do the visuals like suggested to see which is not squirting.
08-03-10, 06:40 PM
#22
The Racing Beat idle jet holder has a small hole drilled in the top. To act as an air bleed. Do you have the idle jet holder with hole on top? If not, and if you're running the RB spec'd 75 idle fuel jet then you're running horribly rich on the progression circuit which is also the light throttle circuit. And it will run like ****.
Take the air filter off and look down each carb throat while playing with the throttle. Make sure the accelerator pump jets spray the instant you crack the throttle.
Also I know you're not using the RB spec'd 39mm chokes in a 40mm carb as none that size were ever made. So what size chokes are you running? Either way with <39mm chokes and jets for a 39mm choke setup you will run rich.
wideband air/fuel gauges help immensely.
Take the air filter off and look down each carb throat while playing with the throttle. Make sure the accelerator pump jets spray the instant you crack the throttle.
Also I know you're not using the RB spec'd 39mm chokes in a 40mm carb as none that size were ever made. So what size chokes are you running? Either way with <39mm chokes and jets for a 39mm choke setup you will run rich.
wideband air/fuel gauges help immensely.
08-03-10, 10:12 PM
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Alrighty well floats have been re-done to spec. Also I put in a Carter fuel pump that pushes 72gph and is regulated to 2.5psi. So far nothing has changed however. I checked for clogs as well in the emulsion tubes and there was nothing to be found there. I did however find that the set screws for the venturis (which i measured at a diameter for 40mm) were not tight any longer and i could physically slide the venturis around inside the throats. I will have to get that fixed and check again to see how it runs.
I did also try to run it without any venturis at all, which seemed to different as well, however there were also no trumpets or air cleaner on at that time either.
I'm not sure if my idle jet holders have holes in the top, I'll have to go look tomorrow. Is it just drilled right in the center downward?
I did also try to run it without any venturis at all, which seemed to different as well, however there were also no trumpets or air cleaner on at that time either.
I'm not sure if my idle jet holders have holes in the top, I'll have to go look tomorrow. Is it just drilled right in the center downward?
08-04-10, 08:45 AM
#24
Waffles - hmmm good
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Go thru the gruntled site and read it some more. RB did a few mods to get the 48
to work well with a rotary. Since your using a 40mm carb some things may be
different but I suspect a lot of the same mods would apply. Also note that some
Dells have extra emissions crap that may need to be side stepped as well.
Get a hold of the Tuning Weber and Dellortos book as it details some of these
issues for the various Dell models. Your going to need patience as this will take
some experimenting to get it right.
This is why I bought my Dell from RB. I don't mind paying for the engineering
work they did to get it right.
to work well with a rotary. Since your using a 40mm carb some things may be
different but I suspect a lot of the same mods would apply. Also note that some
Dells have extra emissions crap that may need to be side stepped as well.
Get a hold of the Tuning Weber and Dellortos book as it details some of these
issues for the various Dell models. Your going to need patience as this will take
some experimenting to get it right.
This is why I bought my Dell from RB. I don't mind paying for the engineering
work they did to get it right.
